Walk Softly – Feels like? Not Sure I Understand

by Geoffrey Carpentier

Summer is upon us, and the news is abuzz with broad and confusing statements about our weather and our climate. According to newscasters, everything is somehow linked to climate change – even when it isn’t. That makes some sense as we tend to react to sensational news, but do they really have to instill whimsical suggestions in their broadcasts to convince us how we should be reacting to weather? I must admit I’m often more confused than informed after listening to some of our weather broadcasts. One which irks me is the reference to the ‘real’ temperature versus the ‘feels like’ one.

I grew up in a simpler time, when it was hot or cold, when it just snowed or rained or the sun shone, or it didn’t. But now I must contend with heat domes, polar vortexes, derechos, bomb cyclones, thundersnow, fogbows, gravity winds, firenadoes and literally hundreds more! But still, I wonder why I must take a real thing like temperature and then think in abstract terms to create an imaginary ‘feels like’?

I did some research and found meteorologists use a precisely calibrated thermometer under controlled conditions, to take away some complicating influences such as wind, in order to measure the actual temperature of the air in Fahrenheit, Celsius or Kelvin – so far so good. But then they factor in other variables to determine the ‘feels like’ temperature. These variables include speed and strength of wind, the actual temperature of the air as described above, the local relative humidity, and the rate of heat loss from a clothed human body. Okay, makes sense, sort of, but how does it factor in differences in individuals’ responses to heat (or cold), as people respond differently to temperature extremes? I, for one, don’t sweat much and have a very high tolerance for heat, although my cold tolerance seems to be diminishing with age!

These days, the National Weather Service seems obsessed with telling us how we should feel when it is sunny and hot; so they now offer us the Heat Index to let us know how hot we think we are. This is a mechanism to combine the actual temperature with relative humidity to determine our response to these temperatures. So, to explain, if there is no humidity, the air should feel like the real temperature, but if you add in humidity, we will perceive the temperature quite differently. For example, if the ambient air temperature is 28 °C and the relative humidity is 65 percent, we feel like it’s 30 °C. Now, increase the relative humidity to 95 percent, and now we think it is 34.7 °C.

Okay, but why do I actually feel hotter when the relative humidity is higher, even though the real temperature is unchanged? Is there any actual science behind this? Well, there is science that we should consider. Humans sweat to cool off. So, we rely on the ambient temperature around us to cool our skin when exposed to higher temperatures. Sweat absorbs heat from the surrounding air, which then evaporates off our skin, leaving us with a cooling sensation. Known as evaporative cooling, this is a fail-safe mechanism to help us cope with excessive heat. Now, if the air is humid, it contains a lot of moisture already and therefore cannot absorb as effectively as much of our sweat, and we feel hotter. Okay, I think I’m starting to understand this a little better now.

A similar concept exists to explain why we feel colder at lower temperatures. Well, yes, there are similarities, but it’s not relative humidity which is the deciding factor; it’s wind. So now we might think about wind chill. If we are properly clothed and protected, and the wind is low, we feel toasty as the hotter air in our bodies rises to the surface of the skin and warms the proximal air, so we stay warm. But increase the wind on exposed surfaces, and suddenly we can’t generate enough heat to warm this fast-moving air, so we feel colder or chilled. Okay, got it! It’s hot today, so I feel like a cold drink!

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.